Optical recording of responses to odor in olfactory structures of the nervous system in the terrestrial mollusk Helix.

Electrophysiological methods and optical methods based on the use of potential-sensitive dyes were used to record stable rhythmic oscillations of local potentials in the olfactory structure (procerebrum) of the pulmonate mollusk Helix: these oscillations were generally similar to those previously observed in slugs. Odor had the effect of transiently altering rhythmic oscillations to generate an individual pattern. This is the first study describing the recording of procerebrum potentials evoked by presentation of odor, with mapping of the areas of propagation of these potentials relative to the areas of propagation of rhythmic oscillations. The boundary of the propagation of the evoked potential was essentially similar to the projection of the neuropil, and rhythmic oscillations were recorded in the projection layer of procerebrum cell bodies. Evoked potential waves appeared in areas corresponding to the site at which the olfactory nerve enters the cerebral ganglion (of which the procerebrum forms a part) and were propagated in the procerebrum neuropil towards the cell body layer. Evoked potentials did not provoke out-of-phase waves of rhythmic oscillations.